1. Field of the Invention
The present invention is directed to a fuel processor, and, more particularly, to a control system for a fuel processor.
2. Description of the Related Art
Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion for use as fuel for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Thus, many types of fuels can be used, some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a relatively pure hydrogen stream used to fuel the fuel cell.
Although fuel cells have been around for over a hundred years, the technology is still considered immature. The reasons for this state are many and difficult. Recent political, commercial, and environmental conditions have, however, spurred an increased interest in fuel cell technology. The increased interest has, in turn, generated a heightened pace of technological development.
However welcome the heightened pace of development may be, it presents problems of its own. Fuel cell designs, particularly those with fuel processors, are typically complex. Consider the fuel processor design illustrated in U.S. patent application Ser. No. 10/006,963, entitled “Compact Fuel Processor for Producing a Hydrogen Rich Gas,” filed Dec. 5, 2001, in the name of the inventors Curtis L. Krause, et al., and published Jul. 18, 2002, (Publication No. US2002/0094310 A1). The anode tailgas oxidizer temperature in this design is a function of catalyst loading, air flow and its space velocity and oxygen to carbon ratio at given space velocities. The sheer number of factors, in itself, makes control of this temperature a difficult task. Furthermore, a change in fuel type—for example, from natural gas to hydrogen—dramatically affects all these variables. Thus, the difficult control problem is exacerbated as the fuel processor design changes.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.